Magnetic Suppression for a Possible Fe-poor Organic–inorganic Hybrid Superconductor Fe14Se16(tepa)0.8 (tepa = Tetraethylenepentamine) with a Superconducting Transition at ∼42 K

Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures ( TC ), but also for understanding the origin of iron-based superconductivity. Here, we report a new Fe-poor organic-inorganic hybrid material Fe14 Se16 (tepa)0.8 with a paramagnetic-diamagnetic transition at -42 K grown by a hightemperature organic-solution-phase method with soluble iron/selenium sources in a tepa solution, alternative to previous intercalation strategies. The Fe14 Se16 (tepa)0.8 phase is in a tetragonal layered hybrid structure with a nanoplate shape. Composition analyses reveal a Fe-poor characteristic of the hybrid in contrast to previous FeSe-intercalated superconductor, and selected area electron diffraction pattern is featured by Fe3 Se4 superstructures with a root 2 x root 2 of Fe vacancy order. Ab initio density functional calculations show that minus Fe3 Se4 ions are stable in the hybrid and -0.25e-/Fe0.75 Se is obviously larger than the reported values of approximately 0.2e-/FeSe in other FeSe-intercalated superconductors. Typical hysteresis loops and temperature dependence of dc/ac susceptibilities of the Fe14 Se16 (tepa)0.8 measured below -42 K suggest a presence of the Meissner effect in this material. Effects of synthesis conditions on structures and magnetic properties of the hybrids show a magnetic evolution from a long-range ferrimagnetic (FIM) order of Fe14 Se16 (tepa) to a coexistence of FIM and superconducting (SC) orders of Fe14 Se16 (tepa)0.9 and an SC order of Fe14 Se16 (tepa)0.8 . X-ray absorption spectrum (XAS) confirms the presence of ferric/ferrous irons. M & ouml;ssbauer studies reveal that the high- TC superconductivity originates from a suppression of the FIM order through tuning the spin states of irons from high-spin Fe3 + ( S = 5/2) and Fe2 + ( S = 2) in the Fe14 Se16 (tepa) to low-spin Fe3 + ( S = 1/2) and Fe2 + ( S = 0) in the Fe14 Se16 (tepa)0.8 . Although no zero resistance is detected even at a temperature of 2 K, the resistivity at 2 K decreases by more than 1600 times compared to that in a normal state calculated by a variable range hopping (VRH) model, suggesting that the high- TC superconductivity of Fe14 Se16 (tepa)0.8 is possible. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.